Icahn Enterprises has announced plans to sell up to $400 million worth of shares through an 'at-the-market' offering program. This move has led to a significant decline in the company's stock, which has dropped nearly 10% and is heading towards a 21-year low. The stock has already fallen 12.5% in a single day following the announcement. Carl Icahn's investment firm filed with the U.S. Securities and Exchange Commission to proceed with this share sale.